Networked Audiovisual Distribution Technologies

By Mike Pedersen, CTS-D, CTS-I, Audiovisual Experience Manager, Information Technology Services, Iowa State University

There is a growing debate among professional audiovisual (Pro AV) specialists regarding AV and information technology (IT).  Has Pro AV fully become a branch of IT?  The “AV is IT” side argues that the convergence of AV and IT is complete with the near ubiquitous inclusion of network ports on Pro AV hardware primarily for remote control applications.  The opposing side would say that unique areas of expertise, such as acoustics and optics, and dedicated AV connectivity technology, such as HDMI, SDI, or MADI, still distinguish AV from IT.  No matter which side they fall on, Pro AV experts all agree that networking of Pro AV hardware is now the de facto design methodology.

However, the future of Pro AV signal transfer is clearly destined for packet-switched network solutions such as the now ubiquitous Internet protocol suite (TCP/IP). In the Pro AV community, this is known as AV over IP or AVoIP.

Historically, the transmission of video was accomplished using standard analog connectivity using coaxial connectors (RCA, BNC) or the once ubiquitous VGA (HD15) connector.  This was followed by a set of dedicated digital AV connectivity solutions starting with DVI and now primarily using HDMI, DisplayPort, and HDBaseT.  HDBaseT is an AV transmission solution that uses standard shielded category cable but operates on a non-networked proprietary point-to-point protocol.  Using these analog or digital AV solutions, systems that require multiple AV sources to be able to be routed to one or more displays utilize dedicated AV switchers that typically come in fixed sizes from 2 input/1 output (2×1) up to 16×16.  Larger solutions up to 128×128 have also been developed, but they are becoming extremely rare.  The obvious downside to these solutions was their fixed I/O size.  If you had a 6×1 AV switcher and needed to add a 7th input, you would have to replace the entire unit.  There are also cable length limitations with HDMI and DisplayPort that create added challenges to system design; this is one of the reasons HDBaseT was developed.  Despite those cons, these dedicated AV switchers are still widely in use.  Here at Iowa State University, we still install them in nearly every classroom due to their cost-effectiveness.

However, the future of Pro AV signal transfer is clearly destined for packet-switched network solutions such as the now ubiquitous Internet protocol suite (TCP/IP).  In the Pro AV community, this is known as AV over IP or AVoIP.  There is a growing set of Pro AV solutions that utilize the network as the transmission protocol for Pro AV signals.  Before going too far, it should be clarified that there are distinct differences between professional AV over IP solutions and the streaming media solutions that are taking over the home entertainment space.  While most streaming media uses the highly compressed H.264 or H.265 protocols, Pro AV systems have more stringent requirements for both latency and quality.  Pro AV is a local solution that requires low latency between experiencing the presenter in person and seeing or hearing them over the audiovisual systems.  In addition, in many cases, Pro AV requires much higher quality which functionally means much less compression and higher bandwidth.  These requirements lead to the need for a different set of protocols.

Enterprises receive several benefits from using AV over IP solutions.  The first benefit is flexibility.  To support multiple input sources and multiple display destinations, they need to buy the exact number of encoders or decoders; they are no longer stuck with fixed AV switcher sizes.  If they need to add a new device to the system, they simply add an additional encoder or decoder as needed and connect it to the network.  Granted, network switches also have a fixed number of ports, but it is much easier and more cost effective to buy oversized network switches to allow for future growth, and network ports are flexible and not strictly designated as an input or an output.  Another benefit is standardization.  Instead of having many different sized audiovisual switchers, the audiovisual distribution consists of only three parts: encoders, decoders, and network switches. This simplifies stock for both ongoing projects as well as spare parts.  A third benefit is functionally removing any distance limitations.  An audiovisual source could be seen or heard anywhere within the building or, with careful planning, anywhere on an entire campus.  We have two entire buildings here at Iowa State University where audiovisual content can be distributed widely, making large events or attendee overflow needs extremely easy to manage.

The key to success in using AV over IP solutions over an enterprise network is planning ahead for the topology, bandwidth, multicast, and quality of service (QoS) needed to support AV over IP.  The high-level topology decision is between creating a dedicated independent network for the AV over IP traffic or adding the AV over IP traffic to the general core network.  Of the two buildings mentioned above, each building used one of the two topologies.  In practice, both have worked very successfully, although less overall configuration tweaking is required on a separate dedicated AV network.  For bandwidth, an uncompressed, full-color, 1920 x 1080 resolution image refreshed at 60Hz with full color requires 4.46 Gbps, with minimal compression to maintain image quality; that can easily fill all the bandwidth on a one gigabit network connection.  Careful planning must be completed to ensure sufficient core network switch capacity.  For multicast, the network engineers need to determine which switch will serve as the IGMP querier; in a situation where multiple network switches are involved, one switch is designated as the querier, and all multicast video traffic has to pass through that switch.  This can require increased link bandwidth between switches depending on the topology of where the AV over IP encoders and decoders reside.  Finally, to ensure the minimal latency and high quality required, QoS should be enabled on the network and the AV over IP traffic should have a high priority.

Residential AV trends often dictate where Pro AV manufacturers move their product lines, and this will be one of those cases.  Most casual home entertainment users are increasingly moving away from cable and instead using streaming services to get their content.  With almost all TVs now having built-in support for streaming services, many people will no longer need to connect any external peripherals to their TV; just plug into power and connect to the WiFi.  While Pro AV has different requirements, as discussed above, this trend of transmitting AV content via the network is a trend that Pro AV will ultimately follow.  AV over IP will be the primary Pro AV transport mechanism in a few years as usage continues to increase and costs subsequently decrease.  It is important for every IT and AV professional to get familiar with the core concepts around the technology so they can enjoy the benefits it can provide.